Separation process



Aug. 7, 1945. A. s. CARTER ET A1. 2,38L38 f SEPARATION PROCESS Filed May 25, 1941 Alberl' Carez" l AAlber? V/Vz'llef?, Jr:

lNvENToRs MMM? ATTORNEY products resulting from pyrolysis; still more par- Patented Aug. 7, 1945 Albert S. Carter' und .All V. iilii 31?., twillY mn, Dei., molan-sl Company; ration ci @ein l te E. il. dus Pent de Ne Willa, e corpospdsn y es. resi. sensa No. ceases This invention relates to processes for the separation of pyrolysis products; more particularly, it relates to the separation of diolefines and halogen substituted dioleines from the gaseous byeticularly, it relates to the separation of 1,3-butadiene and chloro-1,3-butadiene, the chloro-bu- .tanes and chlorobutenes. from which they are termed by pyrolysis. from the hydrogen chloride and other so-called permanent gases formed as by-products in the pyrolysis procesa it is l'rnown that butadiene may result from the high temperature pyrolysis of chlorcbutene and dichlorobutane in the absence of acid acceptors. ier example, by the thermal treatment of 2,3- dlchlorobutane at 60o-700 C. for a short contact time such as 0.3 second in packed or unpacked tubes of inert material. It is also known that ii-chloro-LS-butadiene results from similar treatment of 2.2.3-trichlorobutane -or from dlchlorobutenes resulting from the chlorination of 2- chlorobutene or from the dichlorobutenes resulting from the incomplete pyrolysis `of 2,2,3tri cblorolavutai'ie.` These pyrolvtic procedures result in the diolenne or chlorodioleiine mixed with a 2 variable amount of intermediate unsaturated chloro compounds. hydrogen chloride, and in some cases, very small amounts of methane or hydrogen' orother so-called permanent gases. In the processes of the prior art. it has been suggestedjthat the 1,3-butadiene or chloro-l',3 butadiene, which hereinafter will be referred to as the "conjugated diene's." and the incompletely converted unsaturated chloro compounds be separated from the ivy-product gaseous compounds; l namely, hydrogen chloride and possible small amounts of other permanent gases by cooling or fractional distillation. For the complete removal of these materials from the permanent gases by fractional distillation or by fractional 4 condensation,- either compression or low tempera. tures are required.` Even in the absence of hydrogen and methane, it is necessary to approach the temperature and pressure of liquid hydrogen 4 chloridev in order .to condense completely thev organic materiall from 4the byproduct hydrogen chloride. Low temperature -refrigeration and compression of this corrosive gaseous mixture are expensive and an alternate process is desirable. It has also been proposed in the prior art to pass the gaseous mixture after a.v preliminary condensation throughwater scrubbers inwhich the hydrogen chloride is dissolved. thereby assisting in the complete condensation of the coniugated diene. In this process. the hydrogen s im.. sessi chloride is recovered as a dilute aqueous solution v and its by-product value is impaired. .The object of the present invention is to provide a new method of separating the "cndusted dishes and the incompletely converted reactants i'roin the by-product hydrogen chloride without the disadvantages of the prior art. This object 'has been accomplished by scrubbing the products of pyrolysls with a chloro hydrocarbon capable.

of conversion by pyrolysis to the "conjugated diene" or, in other words, by the absorption of the "conjugated dienes" and the remaining in-- completely converted reactants, from the byproduct hydrogen chloride, by absorption of said "conjugated dienes and reactants in the raw materials for the pyrolysis from which,they are recovered in the normal course of the operation without resort to4 special treatment. We have found that the chlorobutanes and the chlorobutenes capable of being subsequently pyrolyzed to the conjugated dienes" are excellent solvents for the conjugated dienes and capable of absorbing them from gaseous mixture oi' hydrogen y chloride without absorbing, substantial amounts s of the hydrogen chloride itself. For the purpose of absorptive separation of the conjugated dienes" from hydrogen chloride. it is desirable to have an -absorptive medium' possessing a lower vaporl pressure than the conjugated dienes themselves; in fact, '1 a sumciently low vapor pressure that the loss due to evaporation inthe uncondensed stream of hydrogen chloride will be small. It has been found that these properties are satisned by the raw materials subsequently used in the pyrolysis for the production of "conjugated dienes."

'For example. in the production of LxB-buta-` diene by pyrolytic procedures, the vapor pressure rial in the pyrolytic procedure is of the order of 0v millimeters of mercuryor less at room temperature. Therefore, it may be used to scrub the by-product hydrogen chloride without substantial loss by evaporation and. if desired, the temperature of the absorption system can be reduced somewhatfbelow room temperature and this loss materially reduced. In the manufacture 'of `chloro l,3butadiene by the pyrolysis of 2,2;3- trichiorobutane, the vapor pressure of the starting material is less than l0 millimeters at room temperature. f

'- The accompanying drawing, consisting' of a -single gure. is a now sheet of the process. the 6' appratus and its arrangement being diagramf m c' v of the di-chlorobutane used as a starting mate- Y f of the unreacted raw materials and products are condensed. The gases and liquids from I. enter the absorption column l. In l,the products from the pyrolysis contact the unreacted chloro compounds which are introduced into the top of the column from the storage tank I through line t and precooler 'I. Unabsorbed gases leave column l via vent 8 and the liquid products in column 5 pass down through heater t in which the temperature is maintained at or near the boiling point of the "conjugated diene in order to volatilize the last small amoimt of absorbed hydrogen chloride. The liquid product is discharged into the column II.- 'I'he liquids in column I I are boiled by-means of a heater I3 at the bottom, distilling oi! the "coniugated diene" product through condenser Il and liquid line I2.Y This column may be any conventional fractionating column equipped with a total condenser and reflux runback of the usual type to divide the condensate between I! dure can be carried out in essentiallythe same manner. I

A further modication which has been found to assist materially in the complete removal of organic productsifrom the by-product anhydrous hydrogen chloride is to introduce all of the fresh chlorinated tdw material into the top of column Sthroughlinen insteadofintotank I through line Il. In manner, the scrubbing liquid introduced at the top of column i contains only the higher boiling raw materials prior to DyrUly- I sis and is not dihited with some of the more volatile intermediate' roducts present in storage tank andthe reilux line .Il returning to the column.

The undistilled liquids from column Il are discharged continuously into the storage tank Il from which they are pumped by means of pump Il back to storage tank I for further pyrolysis.

-In the operation of the apparatus illustrated for the manufacture of conjugated dienes, unconverted chloro compounds are recovered from the' "conjugated diene" product in column Il. Byproduct hydrogen chloride issues from vent l essentially free of "conjugated diene and unconof chloro compounds through heater 9 and 'column Il." yIn column Il, the 2chloro .1,3buta diene is .distilled olf through line I! andthe mix ture of unconverted 2,2,s-trichloroputane and dichlorobutene which collects in tank 'Il is subsequently pumped by means of pump Il into the original tank I. Recirculation of the recovered material results in a variable composition of the nscemary to introduce. fresh raw material at Il to replenishfthe stockt Inthemanufacf of 1,3-butadiene by this procedure', tank I he charged initiallyA with dichlorobutane such as -dichloi'olntanc and a similar openting cyclo carriedout. Obviously. in the manufacture of 1,3-butadienc, the temperatures in l, l, and in thel bottom of' column Il should belower than the respective temperahn'es viu the manuzum or shim-'1annuaire but the proce- I. In this case, e liquid feed through line II may or may not be diluted with further liquid from tank I as desired.

In order that the process may be more fully4 Example I Using the apparatus illustrated in the gure, introducing fresh chloro raw materials at IIS and precooling the liquor at 1 to 20 C., the cyclic operationl was carried out for the pyrolysis of v2,3- dichlorobutane using a contact time of 0.3 second and a silica pyrolysis tube held at 650 C. In this case, column l was iacketed with brine at 15 C. to 20 C. over the upper two-thirds' of its length andthe introduction of the crude material from condenser 4 was made below this brine jacket. During this operation. the heater I l at thebottom of column Il was maintained to give a liquid temperature of approximately 100 C.

During this operation, each mole of 2,3-dichlorobutan'e introduced into I gaveapproximately 1.75 moles of hydrogen chloride at outlet l and a. liquid condensate consistingof approximately 0.8 mole of Lil-butadiene and 0.15 mole of chlorobutene at outlet I! with the liquid feed at the top of column l held at substantially 20 C. Theanhydrous hydrogen chloride issuing at l contaixled only a fraction of a per cent of organic mate Emmple II 'The apparatus illustrated in the figure was mf ductedthroughasilica pyrolysistubemaintained v at 650 C. at a contact time of 0.3 second, then tocondenser linwhich the products were cooled to approximately room temperature. Column I whichwasinchcsindiameterandlbfeetlong waspackedwithporcelainringsandwasfedonly withthefreshtrichlorobutaneaddedtoreplsoe that-consiunedinthereaction. Duringtheflrst `periodof the operation, 2-chloro-L3-butadiene issuedfromoutlet I2 at therateofapproximately 0.20 pound mole per hour and hydrogen chloride issued from line I, at the rate of amroximatcly 1.0 pound mole per hour. As the operation was continued due to the recirculation of partially converted material (dlchlorolrutene). the rate of creased to over 0.25 pound mole per hour and the production of hydrogen chloride at 8 decreased to 0.77 pound mole per hour. Examination of over 99 per cent hydrogen chloride containing approximately 0.6 per cent chlorinated hydroapproximately 0.60 to 0.70 mole of -2chloro-l,3

butadiene, approximately 2 moles hydrogen chloride at B, carbon deposited in 3 and equivalent to approximately 0.05 to 0.10 mole of trichlorobutane, and a residue remaining in vaporizer 2 analyzing to a chemical composition equivalent 'to polymerized 2chloro-l,3butadiene in an amount of approximately 0.25 to 0.3 mole.

Example III An apparatus similar to the figure was constructed, precooler 1 at the top of column 5 being a low temperature dephlegmator held at --70'J C. capable of giving substantial reflux in column 5 consisting of condensed intermediates and raw materials. For the purpose of analysis, the gas issuing from line 8 was conducted into an analytical absorption system provided for the. measurement of hydrogen chloride, permanent gas, and water-insoluble liquid product. For the purpose of analytical examination, the product was removed from the bottom of column 5, omitting column I0, tank Il, and the recirculating pump l5.

Nine hundred and eighty-three (983) grams of 2,2,3-trichlorobutane was volatilized in 326 minutes and passed through a pyrolysis tube .constructed of copper held at 480 C. with a contact time of 8 seconds. The gas issuing from outlet 8 was found to contain 129.2 grams hydrogen chloride and a few cc. of permanent gas. The liquid product issuing fromthe bottom of the column weighed 821.4 grams. The total accounted for,

therefore, was 950.7 grams or 96.7 per cent of the total starting material, the loss being due to a small amount of carbonization or handling losses in the vaporizer and sample-collecting vessels.

The separation process is applicable to the py-4 dichlorobutene obtained by chlorinating 2-chloro- 2-butene as described in copending application Serial No. 336,626. It is also applicable to the products obtained by the pyrolysis of 1,4-dichloro-2-butene which results in 1-chloro-1,3- butadiene and of other chlorobutanes and chlororeturned from It via I5 tc'.

ciency of the removal of carbonaceous material `from the anhydrous hydrogen chloride gas stream may be enhanced by precooling at l or by cooling in column 5. It is also Within the scope of the invention to operate the apparatus at pressures above atmospheric to facilitate condensation of the products,- particularly in the c ase of butadiene, which boils at 4 C. to 5 C. It is also within the scope of the invention to operate column l0 at a, different pressure from co1- umn t. This has been particularlyadvantageous in the manufacture of chlorobutadiene which Y polymerizes readily at its atmospheric boiling point. In this case, we may operate column iii under a pressure of, for example, 100 mm. of Hg, the residue collecting in it being returned to the system under pressure by means of pump I5. It is also within the scope of the invention to introduce other accessory equipment which may improve the quality of the product or facilitate the operation. For example, steam may be introduced in column l0 to provide for steam distillation of the products, adding at the same time suitable drying equipment for the liquor Apparatus may be -introduced between heater 9 and column i0 to neutralize the remaining traces of hydrogen vchloride existing in the liquids discharged from ses column 5.

Under certain conditions, it has been found advantageous to introduce a separator under condenser l capable of separating liquids which lare introduced directly into column' i0 from'the of the present invention. The design of column may followk conventionalgwell-known lines ohviousto any one skilled in the art. The rate of liquid Aflow at 6 may be determined by conventional calculations or it may be determined experimentally by observing the rate at which the loss of organic material at t becomes a minimum. It will be found that the loss of organic material at B decreases with an increase in liquid flow vat 6 until a minimum is reached which will approximate the quantity calculated from the partial pressure of the liquid introduced at 6 at the operating temperature. for example, that the liquid flow through t should be at least 200 pounds per hour per square foot of cross section in column 5 in the normal operation of the examples cited, Higher liquid rates are advantageous.

It is clear that, while the process is continuous and cyclic in that each step must follow the 1 preceding step in the order set forth, a time lag butenes capable of producing 1,3-butadiene and chloro-1,3-butadienes. These enes to which the process is applicable may be expressed by the formula @Hfs-Cle wherein :c is a member of the group consisting of o and 1.-

'I'he raw materials are chlorinated straight-chain hydrocarbons of the formula Gamen-nchen) wherein :c is the same as before and n is a member of the group consisting of 1 and 2. These formulae clearly indicate that the product is obtained by removing one or two moles of hydrogen chloride from the raw material.

As indicatedv in Examples I and 1I, the emmay occur between various steps. Thus, for example. the chlorinated hydrocarbons collected in storage tank il may be pumped intennittently by pump |15 to storage tank I instead of being pumped in a steady stream.v Accordingly, the

terms "continuous and continuously are used in this application to include a process having intermittent operations of this nature.

It has been found,

1. Process which comprises continuously producing hydrogen chloride and a conjugated diene `of the formula ciHanClr wherein a: is a small whole number of the group consisting of and 1 by pyrolyzing, in a pyrolysis zone, at least one chlorinated straight-chain hydrocarbon of the formula ClHM-Cluwzi wherein :i: is the same as above and n is a small whole number of the group consisting of 1 and 2, continuouslyvpassing the gases from the pyrolysis zone into an absorption zone, continuously. passing more chlorinated straight-chain hydrocarbon, of the above formula, in the liquid phase into said absorption zone. continuously venting gaseous hydrogen chloride from said absorption zone, continuously passing the liquid phase from said absorption zone into a fractionating zone, continuously removing the said conjugated diene in the vapor phase from said fractionating zone, continuously withdrawing the non-vaporized liquid from said fractionating zone, and-continuously recirculating the non-vaporized liquid to the pyrolysis zone. y

2. Process which comprises continuously producing hydrogen chloride and a conjugated diene of the formula CiHus-Cle wherein is a small whole number of the group consistingof 0 and 1 by pyrolyzing, in a pyrolysis zone, at least one chlorinated straight-cham hydrocarbon of the formula C4H e+ne Cl n+z wherein :c is the same as above and n is a small whole number of the group consisting of 1 and 2, continuously cool-A ingthe gases from the pyrolysis zone, continuously passing the resulting mixture of gas and liquid into an absorption zone, continuously passing more chlorinated straight-chain hydrocarbon of the above formula in the liquid phase into said absorption zone near the top thereof, concontinuously cooling the gases from the pyrolysis zone, continuously passing the resulting mixture of gas and liquid into an absorption zone, continuously passing more of said mixture of 2,2,3-trichlorobutane and dichlorobutenes, in lthe liquid phase, into said absorption zone near the top thereof, continuously venting gaseous hydrogen chloride from near the top of the absorption zone,

tinuously venting gaseous hydrogen chloride from near the top of the absorption zone, continuously passing the liquid phase from near the bottom of said absorption zone into a heating zone held at a temperature near the boiling point of the said conjugated diene, continuously passing the heated liquid into a fractionating zone having a heater at the bottom thereof, continuously removing the said conjugated diene in the vapor phase from near the top of the fractionating zone, continuously withdrawing the nonvaporized` liquid from near the bottom of the fractionating zone, and continuously recirculating the non-vaporized liquid to the` pyrolysis zone.

3. Process which comprises continuously producing hydrogen chloride and 2 chloro-rai-lentadiene by pyrolyzing, in a pyrolysis zone, a mixture of 2,2,3-trichlorobutane and dichlorobutenes, continuously passing the gases from the pyrolysis zone into an absorption zone, continuously passing more of said mixture of 2,2 .3trichlorobutane and dichlorobutenes, ln the liquid phase, into said absorption zone, continuously venting gaseous hydrogen chloride from said absorption zone, continuously passing the liquid phase from said absorption zone into a fractionating zone, continuously removing the 2chloro-1,3butadiene in the vapor phase from said fractionating zone,

continuously withdrawing the non-vaporized liquid from said fractionating zone, and continuously recirculating the non-vaporized liquid to the pyrolysis zone.

4. Process which comprises continuously producing hydrogen chloride and 2-chloro1,3buta diene by pyrolyzing, in a pyrolysis zone, a mixture of 2,2,3-trichlorobutane and dichlorobutenes,

continuously passing the liquid phase from near the bottom of said absorption zone into a heating zone held at a temperature near the boiling point of the 2-chloro-1,3butadiene, continuously passing the heated liquid into a fractionating zone having a heater at the bottom thereof, continuously removing the '2-chloro-1,3butadiene in the vapor phase from near the top of the fractionating zone, continuously withdrawing the non-vaporized liquid from near the bottom of the fractionating zone, and continuously recirculating the non-vaporized liquid to the pyrolysis zone.

5. Process which comprises continuously producing hydrogen chloride and 2ch1oro-1,3buta diene by pyrolyzing, in a-pyro1ysis zone, 2,2,3-trifchlorobutane, continuously passing the gasesA from the pyrolysisvzone into an absorption zone, continuously passing more 2,2,3-trichlorobutane, in the liquid phase, into said absorption zone, continuously venting gaseous hydrogen chloride from said absorption zone, continuously passing the liquid phase from said absorption zone into a fractionating zone, continuously removing the 2-ohloro1,3butadlene in the vapor phase from said fractionating zone, continuously withdrawing the non-vaporized liquid from said fractionating zone, andcontinuously recirculating the non-vaporized liquid to the pyrolysis zone.

6. Process which comprises continuously producing hydrogen chloride and 2ch1orol,3buta diene by pyrolyzing, in a pyrolysis zone, 2,2,3- trichlorobutane, continuously cooling the gases from the pyrolysis zone, continuously passing the resulting mixture of gas and liquid into an absorption zone, continuously passing more 2,2,3 trichlorobutane, in the liquid phase, into said absorption zonelnear the top thereof, continuously venting gaseous hydrogen chloride from `near the top of the absorption zone, continuously passing the liquid phase from near thebottom of said absorption zone into a heating zone held at a temperature near the boiling point of the 2chloro1,3butadiene, continuously passing the heated liquid into a fractionating zone having a heater at the bottom thereof, continuously removing the 2-chloro-1,3butadiene in the vapor phase from near the top of the fractionating zone, continuously withdrawing the non-vaporized liquid from near the bottom of the fractionating zone, and continuously recirculating the nonvaporized liquid to the pyrolysis zone.

7. Process which comprises continuously producing hydrogen chloride and 1,3-butadiene by pyrolyzing, in a pyrolysis zone, dichlorobutane, continuously passing the gases from the pyrolysis zone into an absorption zone, continuously passing more dichlorobutane, in the liquid phase, into said absorption zone, continuously venting gaseous hydrogen chloride from said absorption zone, continuously passing the liquid phase from said absorption zone into a fractionating zone, continuously removing the 1,3-butadiene in the vapor phase from said fractionating zone, continuously withdrawing the non-vaporized liquid from said fractionating zone, and continuously recirculating the non-vaporized liquid to the pyrolysis zone. A

8. Process. which comprises continuously producing hydrogen chloride and 1,3-butadiene by pyrolyzing, in a vpyrolysis zone, dichlorobutane, continuously cooling the gases from the pyrolysis zone, continuously passing the resulting mixture of gas and liquid into van absorption zone, continuously passing more dichlorobutane, in the liquid phase, into said absorption zone near the top thereof, continuously venting gaseous hydrogen chloride from near the top of the absorption zone, continuously passing the liquid phase from near the bottom of said absorption zone into a heating zone held at a temperature near the boiling point of the 11,3-butadiene, continuously passing the heated liquid into a fractionating zone having a heater at the bottom thereof, continuously removing'the 1,3-butadiene in the vapor phase from near the top of the fractionating zonel continuously withdrawing the non-Vapor.- ized liquid from near the bottom of the fractionating zone, and continuously recirculating the non-vaporized liquid to the pyrolysis zone.

9. Process which comprises continuously producing hydrogen chloride and a conjugated diene of the formula @Hm-Cle wherein is a i whole number of the group consisting of 0 and 1 by pyrolyzing, inv a pyrolysis zone, at least one chlorinated straight-chain hydrocarbon of the il S. CAR.

m1? V. WPT, Jn. 

